1. Field of the Invention
The present invention relates to a dynamic communication bandwidth allocation method, a computer-readable medium storing a dynamic communication bandwidth allocation program, and a PON (Passive Optical Network) system, for allocating a communication band in an uplink direction to optical network sections (ONUs).
2. Description of the Related Art
A PON system is known as an optical communication system that connects an optical line terminal (hereinafter, referred to as “OLT” or “station-side terminal”) and plural ONUs (hereinafter, referred to as “subscriber-side terminal”) through optical fibers.
As a developed type of this PON system, a GE-PON (Gigabit Ethernet PON) system to which a Gigabit Ethernet technique used in a LAN (Local Area Network) is applied, and that connects the OLT and the ONU with a communication speed of 1 Gbps or higher, has been put into practical use.
In the GE-PON system, the OLT manages transmission timing and communication bandwidths of the ONUs under itself, to prevent optical signals in the uplink direction from the plural ONUs from colliding with one another on time axis. A technique of dynamically managing the communication bandwidths of the ONUs in accordance with a state of communication traffic is so called, dynamic bandwidth allocation (DBA). Hereinafter, an example of DBA will be described.
In DBA, each of the ONUs requests the communication bandwidth in witch the requested ONU requires, to the OLT. Hereinafter, this requested width is referred to as a requested bandwidth. The OLT receives the requested bandwidths from the respective ONUs, distributes the communication band to the respective ONUs in accordance with ratios of the requested bandwidths of the respective ONUs, and notifies to the respective ONUs.
However, in the management of the communication band by DBA in the above example, a service level agreement (SLA) parameter predetermined for each of the ONUs, such as a maximum allocation band and the like, is not reflected in the allocation of the communication band. In contrast, a technique in which the SLA parameter is reflected on the allocation of the communication band to the ONUs has been known (e.g., Japanese Patent Application Laid-Open (JP-A) No. 2007-129429).
In the technique described in JP-A No. 2007-129429, the OLT distributes the communication band to the respective ONUs in accordance with ratios of the SLA parameter of the respective ONUs.
In the technique described in JP-A No. 2007-129429, the ratio of the SLA parameter is used for the allocation of the communication band and not the ratio of the requested bandwidth. Accordingly, deficiency and excess may occur between the requested bandwidth and the bandwidth allocated by the OLT.
In order to solve this deficiency and excess, in the technique in JP-A No. 2007-129429, calculation for allocating a excess of the ONU in which the communication band is allocated excessively, to the ONU whose communication band is deficient, in accordance with the SLA parameter ratio, is repeated until the excess of the communication band is eliminated.
However, in the technique of JP-A No. 2007-129429, a number of repetitions of the calculation is large, thereby increasing calculation time. Further, if the calculation is terminated before the distribution of the excess ends, an unallocated band occurs, thereby deteriorating band utilization efficiency.